1. Field of the Invention
The present invention relates to a scanning optical system, an image formation apparatus including the scanning optical system and an imaging optical system used in the scanning optical system.
2. Description of Prior Art
In general, an image formation apparatus such as a laser beam printer includes a semiconductor laser as a light source, a polygon mirror as an optical deflector for deflecting laser light flux, and a scanning lens (imaging optical system) for forming an image of a laser light flux deflected by the polygon mirror. As described in Japanese Patent No. 3420956, in a known technique, a refractive lens has been used as a scanning lens. In recent years, however, in view of realizing high dimensional aberration correction and the like, use of a scanning lens having a diffractive surface has been proposed (see, for example, Japanese Laid-Open Publication Nos. 12-2847 and 2005-37561).